1. Field of the Invention
The present invention relates to a color cathode ray tube (CRT), and more particularly, to a tensioned shadow mask with a color selection function, which has dummy bridges with an improved structure, and a color CRT adopting the same.
2. Description of the Related Art
Color CRTs for televisions and computer displays employ a shadow mask (hereinafter, simply referred to as a mask) for accurate landing of three electron beams emitted from an electron gun on each phosphor of a phosphor screen. The mask includes a dot mask with substantially circular apertures a slot mask with parallel elongated apertures, and a tensioned mask to which tension is applied from opposite sides thereof, and having series of parallel strips separated by slits through which electron beams pass.
FIG. 1 shows an example of a tensioned mask. As shown in FIG. 1, the tensioned mask formed of a foil includes a plurality of strips 12 separated by slits 11 having a predetermined interval, and a plurality of tie bars 13 which interconnect the adjacent strips to define the slits 11 at predetermined intervals.
In the mask, the tie bars 13 which interconnect the adjacent strips 12 can reduce a howling phenomenon, which occurs due to mask vibration from external impact, and unacceptable Poisson""s contraction. However, if the vertical pitch PV of the tie bars 23 is too large, that is, if the vertical pitch PV of the tie bars 23 is twice or more the horizontal pitch PH thereof, a reflection image of the tie bars 13 is shown on the screen, which is unpleasant to viewers.
To avoid this problem, U.S. Pat. No. 4,926,089 discloses a tensioned mask as shown FIG. 2. As shown FIG. 2, a tensioned mask 20 includes a plurality of strips 21 separated by slits 22 having a predetermined interval, and tie bars 23 which interconnect the adjacent strips 21. Also, dummy bridges 24, which extend partially between but not interconnecting adjacent strips, are disposed between the adjacent tie bars 23 to separate each slit 21 into sub-slits having a predetermined interval.
In the tensioned mask, due to a technical problem in mask pattern formation, the width WI of the dummy bridges 24 is smaller than the width W2 of the tie bars 23. Thus, the reflection images by the dummy bridges 24 and the tie bars 23 have a slight difference in intensity of light. This difference raises the problem of tie bar visibility, thus deteriorating display image and making viewing unpleasant.
In formation of the phosphor screen on the inner side of a faceplate, as shown in FIG. 3, a tensioned mask and frame assembly is secured to a faceplate 100, and then subjected to an exposure process for forming a phosphor screen 101, wherein an exposure lamp 102 for use in the exposure process is long enough to irradiate a region corresponding to the vertical pitch between adjacent tie bars 23 or that of adjacent dummy bridges 24 of the tensioned mask 20. However, in the phosphor screen formation using the exposure lamp 102, red phosphor, blue phosphor and green phosphor are not completely excited, resulting in black matrix pattens in the nonexcited regions, as shown in FIG. 4. This problem is associated with the offset configuration of the dummy bridges 24 of the tensioned mask 20. In particular, as shown in FIG. 2, the dummy bridges 24 of the tensioned mask 20 extend from a strip 21xe2x80x2 toward the adjacent strip 21xe2x80x3, to define gaps near the strip 21xe2x80x3. Accordingly, regions of the phosphor patterns that correspond to the offset protrusions of the dummy bridges 24, except for regions that correspond to the gaps between the dummy bridges 24 and the strip 21xe2x80x3, are not excited by the electron beams emitted from the electron gun, so that the black matrix remains therein. Such intrusion of the black matrix into the red, blue and green phosphor patterns reduces the emission area of the phosphors, and regions, which are not excited due to the dummy bridges 24 are also shown in a screen, thereby lowering appearance uniformity.
An object of the present is to provide a tensioned shadow mask and a color cathode ray tube (CRT) adopting the same, capable of eliminating intrusion of a black matrix into phosphor patterns during phosphor screen formation, due to dummy bridges.
Another object of the present invention is to provide a tensioned mask and a color CRT adopting the same, capable of eliminating the problem of tie bar visibility.
According to an aspect of the present invention, there is provided a tensioned shadow mask for a cathode ray tube (CRT), comprising: a series of parallel strips separated by slits having a predetermined interval; a plurality of tie bars interconnecting adjacent strips to define a plurality of slits at predetermined intervals; and a plurality of dummy bridges disposed between adjacent tie bars, the dummy bridges extending between the adjacent strips and facing each other, but not interconnecting the adjacent strips.
Preferably; the area of the dummy bridges is equal to that of the tie bars, or the area difference between the dummy bridges and the tie bars is in a predetermined range.
According to another aspect of the present invention, there is provided a color cathode ray tube (CRT) including a faceplate having on the inner side thereof a phosphor screen, a tensioned mask and frame assembly secured into the faceplate, which is an assembly of a tensioned mask and a frame, a funnel connected to the faceplate, the funnel having a neck portion and a cone portion, an electron gun inserted in the neck portion of the funnel, and a deflection yoke installed in the cone portion of the funnel, wherein the tensioned mask comprises: a series of parallel strips separated by slits having a predetermined interval; a plurality of tie bars interconnecting adjacent strips to defines a plurality of slits at predetermined intervals; and a plurality of dummy bridges disposed between adjacent tie bars, the dummy bridges extending between the adjacent strips and facing each other, but not interconnecting the adjacent strips.